Fate of the 14C-labeled herbicide prosulfocarb in a soil and in a sediment-water system

The fate of C-14-labeled herbicide prosulfocarb was studied in an agricultural soil and in a sediment-water system, the sediment part of which was derived from Yangtze Three Gorges Reservoir, China. Time-course studies were performed for 28d and 49d, respectively. Main transformation routes of C-14-prosulfocarb were mineralization to (CO2)-C-14 and formation of nonextractable residues amounting to 12.13% and 10.43%, respectively, after 28days (soil), and 9.40% and 11.98%, respectively, after 49d (sediment-water system). Traces of prosulfocarbsulfoxide were detected by means of TLC, HPLC, and LC-MS; other transformation products were not found. Initial extraction of soil assays using 0.01M CaCl2 solution showed that the bioavailability of the herbicide was considerably low; immediately after application (0.1d of incubation), only 4.78% of applied radioactivity were detected in this aqueous fraction. DT50 values of C-14-prosulfocarb estimated from radio-TLC and -HPLC analyses were above 28d in soil and ranged between 29d and 49d in the sediment-water system. Partitioning of C-14 from water to sediment phase occurred with DT50 slightly above 2d. With regard to the sediment-water system, adsorption occurred with log K-oc = 1.38 (calculated from 2day assays) and 2.35 (49d assays). As similarly estimated from portions of C-14 found in CaCl2 extracts of the 0.1d assays, C-14-prosulfocarb's log K-oc in soil was 2.96. With both experiments, similar portions of nonextractable radioactivity were associated with all soil organic matter fractions, i.e. nonhumics, fulvic acids, humic acids, and humin/minerals. Throughout all sample preparation, the experiments were severely impaired by losses of radioactivity especially with concentration of samples containing water in vacuo. All findings pointed to volatility of parent prosulfocarb in presence of water rather than volatility of transformation products. According to literature data, this behavior of prosulfocarb was not expected, though volatility was demonstrated under field conditions.